The following relates generally to wireless communication, and more specifically to listen-before-talk (LBT) techniques for uplink transmissions from a user equipment (UE) to a base station.
Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems. A wireless multiple-access communications system may include a number of base stations, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE).
Some modes of communication may enable communication between a base station and a UE in a shared radio frequency spectrum band, or in different radio frequency spectrum bands (e.g., in a licensed radio frequency spectrum band and a shared radio frequency spectrum band) of a cellular network. However, in contrast to a carrier in a licensed radio frequency spectrum band, which may be allocated for use by the devices of one public land mobile network (PLMN) and be available to a base station or a UE of the PLMN at predetermined (or all) times, a carrier in a shared radio frequency spectrum band may be available for use by the devices of the PLMN intermittently. This intermittent availability may be a result of contention for access to the carrier of the shared radio frequency spectrum band, between devices of the PLMN, devices of one or more other PLMNs, and/or other devices (e.g., Wi-Fi devices). For some radio frames, a device of a PLMN may win contention for access to a carrier in the shared radio frequency spectrum band, while for other radio frames, the device may not win contention for access to the carrier in the shared radio frequency spectrum band.
Because of the intermittent availability of carriers in a shared radio frequency spectrum band, base stations and UEs may use techniques that provide fairness in coexistence with other users of the shared radio frequency spectrum band, and that still provide reliable communications. For example, such techniques may include establishing radio frame intervals in which a base station may win contention for the shared radio frequency spectrum band and reserve the shared radio frequency spectrum band for some or all of an expected uplink transmission from a UE. Such techniques may increase the likelihood that the UE will win contention for uplink transmissions associated with a radio frame, and it may be desirable in some systems to periodically adjust some parameters associated with reservation of the medium or scheduling of UE uplink transmissions, in order to enhance system efficiency. Efficient techniques for uplink scheduling and channel contention in a shared radio frequency spectrum band may enhance the operation of such networks.